Abstract

We present a theoretical model of photorefractive parametric oscillation that is capable of explaining the occurrence of so-called longitudinal, degenerate, and transversal parametric oscillation in photorefractive crystals. It appears that transversal parametric oscillation occurs in a parameter region that, until now, has been overlooked in the literature. Moreover, we present experiments on the different parametric processes that qualitatively verify our theoretical results.

Figures (8)

Contour plots of the real part of s+ versus X (abscissa) and Y (ordinate) for different values of ε. In all cases the light areas represent unstable regions and the black areas represent stable regions. The contours outlined by dashed curves in each figure represent Re(s+)=0; the other contours represent Re(s+) of 5, 10, 15, and 20 s-1, respectively. The plots are generated from Eq. (19) with the following experimental parameters inserted: E0=14kV/cm,I0=40.7mW/cm2,kp=2π/30µm-1, and m=1.

Diffraction patterns obtained on the screen for various values of ε. In all cases the powerful spot at the left is the directly transmitted spot (zeroth order), whereas the spot at the right is the first-order spot. All spots between stem from diffraction in secondary gratings that arise because of parametric oscillation.

Contour plot of the real part of s+ versus ε and r for X=0.5 and Y=0. In white region (1) DPO is possible, whereas in black region (2) TPO is possible. The same experimental parameters as in Fig. 2 have been used.

Contour plot of Re{s+} versus X and ε for Y=0. The various light regions represent unstable regions; the black area represents stable regions. The contours outlined by dashed curves represent Re(s+)=0; the lighter shaded contours represent Re(s+) of 5, 10, 15, and 20 s-1. White curve (1) marks the maximum of the landscape; black-and-white dashed curve (2) represents the values of X and ε for which the secondary waves fulfill the dispersion relation. The black circles show, for ε=0.22, the X values for the signal and idler waves in the case of eigenwave excitation; the white circles show an example of noneigenwave excitation. The same experimental parameters as in Fig. 2 have been used.